Which of the following measurements is expressed to three significant figures? 7.30 × 10–7 km 0.070 mm 0.007 m 7077 mg

Answer : The correct option is,

Explanation :

Significant figures : The figures in a number which express the value -the magnitude of a quantity to a specific degree of accuracy is known as significant digits.

Rules for significant figures are :

As per question,

has 3 significant figures.

0.007 has 1 significant figure.

0.070 has 2 significant figures.

7077 has infinite significant figures.

Hence, the correct option is,

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol